VSE playhead position variable
The VSE current frame is the same as the current frame for the rest of blender, which is a property of the current scene.

It can be accessed with bpy.context.scene.frame_current and set with bpy.context.scene.frame_set(frameNumber).

The best way to figure out the Python code for a specific property is to find it in the interface and hover your cursor over it, which will reveal the python code. In this case you can hover your cursor over the frame values in a Timeline editor.